In recent years, the field of tree-ring studies has evolved rapidly, to become a key but sometimes controversial tool in measuring past temperatures. D’Arrigo, a leading dendrochronologist, discusses recent advances in methods that have proven the records to be reliable, despite controversies over whether records may be missing or misread during some periods of extreme weather. Furthermore, coverage of samples has spread to the most remote parts of the world, and researchers are in the process of obtaining or expanding records in places like far eastern Siberia, the Himalayas and the subarctic, to make the record stronger.

In the early 13th century, nomadic Mongol herders briefly conquered the largest land empire in history, then receded—and event that has remained in many ways an enigma. Some historians have speculated that environmental factors played a role, but little high-resolution data from that time and place has been available. Now, the authors have obtained tree-ring samples from central Mongolia indicating that the early 1200s were the warmest, wettest time ever in that cold, arid part of the world, which would have enabled the Mongols to raise large number of horses and other livestock needed for conquest. The region soon plunged back into cold, dry conditions—coinciding with the start of the empire’s dissolution. The results are the first step in a long-term project also using lake sediments, historical records and energetics models to examine the Mongol rise to power.

Maps previously produced by members of this group predicted with eerie accuracy the extreme flooding of New York and surrounding areas during Hurricane Sandy. Here, the authors expand and refine their models of potential future flooding by feeding in new data on ongoing land subsidence; changes in ocean circulation; glacial ice melt; and the influence of rainfall, river flow and land storage of water, which may substantially affect flooding in tidal waterways such at the Hudson and Delaware rivers. As part of their work with the Consortium for Climate Risk in the Urban Northeast, the authors are using this data to create risk assessments for tropical and extra-tropical storms for the 2010s, 2050s and 2080s in cities including Boston, New York and Philadelphia.

Public-health professionals are increasingly concerned about the potential impact that climate variability and change can have on infectious diseases. The author’s institution is developing new products to increase the public health community’s capacity to understand and use climate data to battle meningitis and malaria in Africa, outbreaks of which are linked to specific weather conditions. Ceccato presents new and improved products developed for relevant factors including dust, temperature, rainfall and the capacity of vectors such as mosquitoes, for forecasting risks of epidemics. Officials are already using such information to put resources into place ahead of time.

Earth’s landscape is in constant flux, shaped by erosion, climate, earthquakes and other forces. In a new method for reconstructing elevation changes on the landscape, scientists are now isolating leaf wax, kerogen and other organic molecules buried deep in sediments and analyzing their chemical composition. On the Tibetan Plateau, Polissar, a climate scientist, has used this technique to study past elevation of the Namling-Oiyug basin at the southern edge of the Tibetan Plateau. New evidence suggests that this region was uplifted much earlier than previously thought—some 25 million years ago instead of 12 million years ago, as the Indian subcontinent crashed into Asia forming the Himalaya Mountains. An earlier formation for the Plateau suggests that expansion of grasslands in India and Pakistan 8 million years ago was caused by environmental changes other than tectonic uplift.

Melting glaciers in eastern Europe about 16,000 years ago caused massive, repeated flooding of what was then Black Lake—later the Black Sea–according to a new analysis of sediment cores. Together, up to nine floods deposited enough red clay to cover an area the size of Connecticut, Massachusetts and Rhode Island a foot deep, according to calculations by Matamoros. Matamoros’s adviser, marine geophysicist Bill Ryan, speculates that periglacial lakes formed at the edge of the ice sheet as climate warmed. When those freshwater lakes overflowed, they washed vast amounts of soil into Black Lake below. Ryan’s earlier research suggests that Black Lake became the salty Black Sea about 8,400 years ago, as Mediterranean waters rushed in–an event that may have corresponded to the Biblical account of Noah’s flood.

The degree to which Himalayan glaciers may melt in coming years has been the subject of much uncertainty and controversy, since there is little data for many regions. Researchers with this team have been doing arduous fieldwork in the Bhutanese Himalaya. Based on gridded climate data and a robust glacier-melt model, they project that glaciers there will lose 10% of their area in coming decades, even if temperatures remain the same as today. And, if temperatures go up even 1 degree C—well within current projections–about 25% of the area will disappear. These trends would bring declines in meltwater flux of 30% to 65%, respectively. New mapping of glaciers from 2000-2010 shows that glaciers have already shrunk 4%-6%. Bhutan provides hyydropower and irrigation water for far more populous nations downstream, so these changes could have severe consequences. Bhutan is thought to be emblematic of the wider eastern Himalaya, which is strongly influenced by seasonal monsoon precipitation.

When icebergs break off the Greenland ice sheet, they set off measurable seismic signals, and amid the Arctic’s rapid warming, the number of “ice quakes” in the last 20 years has risen steadily. Nettles, a seismologist, shows in a study in press that the quakes are also spreading to the coldest part of Greenland in the north, providing further evidence that the front line for Arctic climate change is shifting poleward. The current analysis stops at 2010, but Nettles expects 2012 to see a record number of quakes. The northward progression of ice quakes means that glaciers are receding to the point that their calving front is now on bedrock—an observation relevant to projections of sea-level rise, since ice dumped into the sea from the grounding line inward contributes to sea level.

Separate teams are studying the U.S. Northeast, Iceland and Oman for potential to store excess carbon within different kinds of rocks. In the New York metro area, test wells have been drilled into the largely sedimentary Newark Basin, and scientists are assessing the possibilities of leakage from any future injections. In Iceland, Reykjavik Energy is already injecting carbon into basalt, a volcanic rock, where it is predicted that natural chemical reactions will turn it into a solid carbonate, thus obviating the threat of leakage; researchers are measuring the reactions as they take place, via boreholes. In Oman, another team is studying peridotite, a deep-earth rock that here has been thrust near the surface, for its potential to perform similar solidification, but 1,000 times faster, if natural processes can be artificially sped up. Experimental drilling is in planning stages.

A five-year project to map earthquake and flooding hazards in the world’s most densely populated nation is revealing a detailed picture of intertwined hidden faults that are building tectonic strain. There is also an apparent history of sudden, catastrophic river-course changes that may be related to earthquakes. Scientists are using seismic imaging, drilling and GPS measurements from a newly installed network of instruments to come up with the data. The project is aimed at helping Bangladesh better assess the hazards, to protect people and infrastructure. Various team members are presenting results.

In light of the disastrous 2012 U.S drought, and indications that some regions may be headed for long-term aridity, the United States needs better forecasts of water availability. Current models account mainly for weather—yet much water is now being pumped from underground for agriculture and urban areas, and this must be factored in to give a truer picture of coming challenges. Using this kind of data, the authors’ preliminary analysis says large parts of the Midwest and southern California and Florida are becoming vulnerable to severe multiyear droughts, due to high water demands coupled with erratic year-to-year rains. By further developing such indices, they hope to strengthen the existing national drought early-warning system.

A hydrofracking waste-disposal well near Youngstown, Ohio, was shut down last year after Lamont-Doherty seismologists linked injections to a series of nearby earthquakes. Kim, who was involved, now says the problems should have been caught months earlier: geophysical logs created when the well was first drilled identified dangerous weak zones in the basement rock–yet waste fluids were injected just above this area. The quakes began within weeks, and occurred in a steady sequence with no aftershocks—signs that they were human-induced. In the wake of the shutdown, the Ohio Department of Natural Resources hasproposed major changes to its regulations. The U.S. Geological Survey this year found a six-fold increasein earthquakes across the U.S. Midwest to be human-related.

As Hurricane Sandy showed, there is an urgent need to better understand how long-term climate change and short- and medium-term climate variability may affect the probability of disastrous floods. Robertson discusses how daily fluxes in weather coming from the Gulf of Mexico drive spring floods in the Midwest; how these fluxes may work on yearly and decadal scales; and how faraway phenomena including the La Nina phase in the Pacific Ocean, and certain phases of the Madden-Julian Oscillation in the Indian and Pacific oceans, can combine with these in certain years to threaten the most extreme floods.